Spiral sweep generator



Oct. 21, 1958 G- VAN Bf KING' v SPIRAL swEEP GENERATOR 2 Sheebs-SheefI 1Filed Feb. 2s, 195e 2K@ 3k m lINVENTOR. Gwenn/v V/m/ 9. //va Oct. 21,1958 G. VAN B. KING sPIRAL swEEP GENERATOR 2 Sheets-Sheet 2 Filed Feb.25, 1956 MEP* SPL SWEEP GENERATOR Gordon van B. King, Convent, N. 3i.Application February 23, 1956, Serial No. 567,236 5 Claims. (Cl. 315-24)This invention relates to means for generating wave patterns to controldeiiection of the electron beam in a cathode ray tube and to the meansthrough which the Wave patterns exercise control of beam deflection.

The invention provides a generating system with cyclically operatingcircuit means for modulating applied electrical waves by imposingthereon a predetermined wave form, the form and frequency of the imposedwaves being respectively determined by the electrical characteristicsand the cyclic frequency of the cyclically operating means. In a morespecific aspect, the invention provides for cyclically operating circuitmeans in the generator to modulate regular sinusoidal input waves byimposing thereon a sawtooth component of lower frequency than the inputwaves, whereby the generator produces trains of output waves ofsinusoidal form, each train within a sawtooth cycle and composed ofsinusoidal waves progressively varying in amplitude according to theslope of the sawtooth component.

The invention further provides for utilization of these generated trainsof Waves as deiiection control waves for controlling deection of theelectron beam in a cathode ray tube through a spiral scanning pattern,one for each train of waves and each spiral pattern having a number ofrevolutions equal to the number of Waves in a train, the revolutionsapproximating circles. The spiral scanning pattern has the advantage ofaffording equal scanning frequency in coordinate horizontal and verticaldirections in contradistinction to the usual zig-zag pattern of Vaseries of high frequency horizontal scans combined with a low frequencyvertical scan. Correlative to the equal horizontal and verticalfrequencies afforded by the spiral scanning pattern, the inventionprovides symmetrical horizontal and vertical deflection circuits withlike, interchangeable components. According to the invention, the trainsof sinusoidal waves of progressively varying amplitude may be used asdeliection control voltage waves applied through a phase shiftingnetwork to symmetrical coordinate deection circuits to cause theelectron beam in a cathode ray tube to describe a spiral sweep patternfor each applied train of deection control waves. The spiral scanningpattern and the symmetrical deflection circuits producing it may be usedto advantage in preference to the usual zig-zag scanning pattern andunsymmetrical deection circuits. As an instance, the spiral scanningpattern and symmetrical deflection circuits have been found advantageousfor use in place of the zig-zag scanning pattern and associateddellection circuits shown in my copending application Serial No.335,944, led February 9, 1953, and dealing with a data processingsystem.

The type of voltage pattern generated according to the invention may beused with suitable circuitry to deect the electron beam in cathode raytubes having either magnetic or electrostatic deection means; it may beused with display type tubes such as Oscilloscopes and ying spot tubes,with camera tubes such as iconoscopes, or with data storage tubes.

2,857,553 Patented Oct. 2l, 1958l The invention provides for recordingthe desired sequence of voltage variations, or desired voltage pattern,on a magnetically coercive medium such as a magnetic drum, disk, tape,belt, or wire, and which may be played back through suitable amplifyingmeans to control the deflection circuits associated with one or morecathode ray tubes for producing the desired scanning pattern in the tubeor tubes. One advantage of first recording the desired voltage patternon a magnetic medium is that it permits great flexibility in the designand production of the exact wave form desired for a particular use.Another advantage is that once the desired pattern has been magneticallyrecorded, it can be played back over long periods of time with permanentsynchronism between the component wave forms entering into the pattern;specifically, between the sinusoidal and sawtooth components of thepattern. Still another advantage of magnetically recording the voltagepattern is that it permits great exibility in playback speed, thusaffording a simple means for multiplying the voltage frequency.

The invention is featured by a synchronous motor to drive the magneticmedium; specically, a magnetic drum, during recording of the voltagepattern; by the use of alternating voltage from the same power linesupplying the motor as the source of the sinusoidal voltage componententering into the composite voltage pattern; by the use of apotentiometer driven by the synchronous motor as the cyclicallyoperating means for introducing the sawtooth component into the voltagepattern; by the use of symmetrical coordinate, horizontal and verticaldeflection circuits for a cathode ray tube; and by the use of a phaseshifting network through which the voltage pattern is applied to thecoordinate deiiection circuits With a phase difference of degreesbetween the voltage applied by the phase shifting network to thehorizontal deflection circuit and the voltage applied by the network tothe vertical deflection circuit, whereby the electron beam in thecathode ray tube is directed through a spiral scanning pattern.

Other objects and advantages of the invention will appear from thedetailed description, the claims, and the drawings.

Fig. 1 is a schematic showing of a typical mechanical layout of theparts of the generator.

Fig. 2 is a schematic Wiring diagram of the circuit connections betweenparts of the generator.

Fig. 3 shows the form of generated deflection control voltage.

Fig. 4 shows the circuit of the deflection system for a cathode ray tubeto which the generated voltage pattern may be applied to produce aspiral sweep pattern.

Fig. 5 shows the form of spiral sweep pattern produced.

Referring to Fig. l, a synchronous motor 1 receives electrical powerfrom an alternating, sinusoidal voltage supply line AC when a switch 2is closed. Motor shaft 3 drives a gear reduction unit 4. The outgoingshaft 5 of the gear reduction unit 4 drives a second, optionallyemployed gear reduction unit 6 which, through an optional clutch 7rotates shaft 8 of a magnetic drum designated MD. Fixed on the shaft 5of the gear reduction unit 4 is a gear 9 which meshes with a gear 10 onthe shaft of slider or wiper arm 11 of a potentiometer generallydesignated P.

It will be brought out in the description of Fig. 2 that the voltagepattern generated, and recorded on drum MD, is the result of equalamplitude sinusoidal waves originating on line AC being modulated by asawtooth wave fc-rm imposed by the potentiometer P during a revolutionof its arm l1. Each revolution of the potentiometer arm denes a sawtoothcycle. The ratio of sinusoidal frequency to sawtooth frequency is theratio of alternating voltage frequency on line AC to the rota` tionalfrequency of the potentiometer arm. Unit 4 principally determines thisratio. Assume, for example, that the motor l1 is a 4-pole motor and thatthe alternating voltagefrequency is 60 cycles per second; Motor 1therefore rotatesY at 30revolutions per second. Assumingl that the gears9 and 10 are of the same diameter, if thegear reduction unit 4- has aratio of 71/2' toA 1, the potentiometer arm rota-tes at the rate of 4revolutions per second. In this interval, 60v sinusoidal waves appear online AC; hence, thel ratio of sinusoidal to sawtooth frequency is ,1*5-to l?, and I5 sinusoidall waves occur during one sawtooth-cycle; Duringeach sawtooth cycle, one complete voltage pattern may be` magneticallysimulated on the. magnetic drum MD. Gear reduction unit 6- determinesthe ratio of potentiometer cycles per revolution ofthe drumand, hence,the number of complete voltage patterns which can be tracked along onefull circle of the drum. vFor example, if unit 6 has a 4 to 1 ratio, thedrum will make one turnV while the potentiometer performs four cycles;therefore, four complete patterns of voltage will be recorded along onecircle of the drum. Obviously, to avoid recording of an incompletepattern on the drum, the number of potentiometer cycles per drum turnmust be an integral number. If only one pattern per drum turn isrequired, the gear reduction unit 6 may be omitted and the drum drivenone-to-one with the potentiometer arm by the gear reduction unit 4.

Each voltage pattern recorded on the drum MD will give rise duringplayback operation to one spiral scanningraster or pattern (Fig. 5) inwhich the number of revolutions or scan lines of the scanning traceequals the number of sinusoidal cycles per voltage pattern. Hence, thespeed of the drum during playback determines the raster frequency andthe scan line frequency. For instance, if there are 4 voltage patternsin a drurn circle, each with sinusoidal cycles, and the drum makes onerevolution per second during playback, the raster frequency is 4 persecond and the scan line frequency is 60 per second. This scan linefrequency is the same as the frequency at which the sinusoidal cyclesare recorded on the drum when the line AC supplies 60 cycle alternatingvoltage.

` In many cases, it is desirable to have a scan line frequency muchgreater than 60 per second. This is readily obtainable by use ofsuitable drive mechanisms for revolving the drum at relatively low speedduring recording and at high speed during playback. For example, if theunit 4 has a reduction ratio of 15:1, unit 6 a reduction ratio of 10:1,and motor 1 is driven at 30 revolutions per second by 60 cycle power online AC, then the potentiometer arm 11 will make 2 revolutions persecond. while the drum makes one-fifth of a revolution per second. Theratio of potentiometer turns to drum turn is, therefore, 10 to 1, and 10complete patterns are recorded along, a drum circle. The sinusoidalfrequency during recordingy is the 60 cycle frequency on line AC andsince the potentiometer arm makes 2 revolutions a second, 3-0 sinusoidalcycles are recorded per sawtooth cycle and a total of 300 sinusoidalcycles is contained in the 10 voltage patterns applied to the drumcircle. During playback, the drum may be run, for instance, at 60revolutions per second, thus providing a raster frequency of 60.0 persecond and a scanning frequency of 18,000 scan l-ines per second. Inother words, the input frequency of 60' sinusoidal cycles per second tothe drum has been multiplied 300 times during playback to produce anoutput frequency of 18,000 sinusoidal cycles per second. The limitationon frequency multiplication is set by the recording requirement ofsuflicient speed of the drum periphery, or magnetizable surface, toenable the 60 cycle sinusoidal waves to be satisfactorily impressedmagnetically. A surface speed of about 5 inches per second is taken as adesirable minimum speed during recording.

.Numerous variations of the basic arrangement shown in, Fig. 3 arepossible. Gear reduction unit 6. may be omitted and its function takenover by the gearing between unit 4 and the potentiometer. For instance,if gear 10 were one-fifth the diameter of gear 9, the potentiometer armwould turn at ve times the rate of the magnetic drum, assuming the drumwere receiving drive directly from shaft S of unit 4; The clutch 7 isdesirable to permit the drum to be disconnected following recording. Thedrum can then be driven at higher speed for playback, either by motor 1through a different transmission than shown or by another motor.

In Fig. 2, line AC and switchv 2 are the same as in Fig. l for applyingpower to synchronous motor 1, though a separate switch may be used. Thesinusoidal voltage on line AC is applied to a suitable step-downtransformer TR1 upon closure of switch 2. The secondary of thetransformer supplies the sinusoidal voltage to the potentiometer Pthrough a resistor R1 and a voltage divider R2'. A capacitor C11combines with RI to form a filter capable of improving the wave form o'fthe transformer' output. RZ affords means to adjust the maximum inputsignal voltage, that is, the maximum amplitude of the sine waves to betransmitted from the secondary circuit of the transformerv to theamplitude modulating means. The amplitude modulating means comprises thepotentiometer P. Voltage from the slider of R2- goes' through resistiveelement Rp of the potentiometer and thence via a resistor R3 to ground.Thev relative values of Rp and R3 determine the degree of modulationeffected. If the maximum modulated, output signalv voltage is to be,say, 20' times the minimum, Rp and R3 are chosenI so that the resistanceofv Rp to that of R3 will be 19 to 1. A resistor R4 is connected betweenthe slider of R2 and a resistor R5 which leads tooutput point 20'. Thevalu'e of R4 governs the base voltage level during the interval in whichthe potentiometer arm 11 is traversing the gap between the ends of Rp.If the base voltage level, at the point 20, is to be zero, 4R4 will bedisconnected from the slider of R2 and connected instead to ground. Ineither case, the Value of R4 should be high compared to the values of Rpand R3 to avoid distortion of the sawtooth form. Typical values areR4-l000 ohms, Rp-l00 ohms, and R3-5 ohms.

Since potentiometer P is used onlyy during generation of the modulatedsinusoidal voltage and its recording on the magnetic drum and may remainidle during playback, the potentiometer may be a low-priced commercialunit such as a molded composition 2-watt unit modified by removal of anyshaft limit stops so as to leave the potentiometer arm free to rotatecontinuously.

During each revolution of the potentiometer in the indicated direction,it progressively increases the proportion of Rp and R3r resistanceinterposed between the slid'- er of R2 and the resistor R5. The effectis to impose a declining sawtooth modulation upon the voltage wavespassed to point 20, with a resulting pattern of modulated voltage suchas indicated in Fig; 3. Obviously, by rotating the potentiometer arm orslider 11 in the reverse direction, an ascending modulation of sawtoothform could be imposed on the input signal. Also, instead of providing aresistive element Rp with linear resistivev characteristics, one havinga different resistance gradient may be used. Thus, a potentiometerproviding a logarithmically tapering resistance gradient or a resistancegradient varying according to any other desired mathematical law may beused. Also, a combination of various potentiometers may be used inseries, the output circuit of one serving as the input circuit to thenext. modulating wave forms may be imposed cyclically on the appliedalternating signal, whereby almost any desiredl resultant form of outputsignal may be obtained'.

The resultant, modulated output signal appearing at the point 20 (Fig.2) ymay be vapplied directly to a utilization device via a capacitor C3,van amplifier 21, and' plugging from terminals T141 and T211 to output'terminals TI Thus any of various and T2 of the generator, and thence tothe input terminals of the utilization device. It is preferred, however,in View of the advantages explained before, to impress the generatedvoltage pattern magnetically on a magnetic medium, such as the drum MD,from which derived voltages corresponding to the recorded pattern may betransmitted to the utilization device through a playback circuit.` Thecircuitry required to magnetically record the generated voltage patternupon the drum MD depends on the type of record-playback head Which isused. If a head designed for handling speech and music is used, anycommercial tape recorder amplifier would be suflicient between outputpoint 20 of the generator and the magnetic pickup head. Such commercialunits are equipped with a recording bias generator and switching meansfor selecting recording or playback operation. It is preferred, however,to use a record-playback head 22 of the very W impedance type such ashandle voltage pulses in electronic computers. For `effectively drivingsuch low impedance head, an amplifier having greater power than theusual tape recorder amplifier is employed, along with a separate sourceof high frequency bias. The higher power amplifier is represented inFig. 2 by the block 21 and the source of high frequency bias by theblock 23 marked Recording Bias Generator. The unit 23 may be aconventional audio oscillator with an output signal of at least 10 voltsR. M. S. Resistor R5 and a capacitor C2 couple the modulating circuitand the recording bias generator to the common point from which theresulting signal is transmitted via C3 to the amplifier 21. The outputof the amplifier, reflecting the applied signal, is transmitted via adouble pole, double throw switch 24 when the switch is in recordposition, reverse to that shown, to the record-playback head 22, causingthe signal pattern to be recorded on the magnetic drum MD. Amplifier 21may be of the type having transformer output with an impedance of 4 or 8ohms. Good results have been obtained by using a watt audio amplifierwith output taken from the 8 ohm terminals to furnish the recordingsignal to a Brush type 1605 head coacting with a magnetic drum having astandard red oxide coating.

Switch 24 is shown in playback position. After the desired voltagepattern has been recorded on the drum MD, it may be disconnected fromthe drive mechanism shown in Fig. 1 and driven by other means, asexplained before, for playback. Preparatory to playback, the switch 24will be thrown from record position to the shown playback position. Thehead 22 will then be in circuit with the playback amplifier 25, theoutput terminals' T1b and T2b of which may be plugged to the finaloutput terminals T1 and T2. A resistor R6 and a capacitor C4 form afilter to smooth out the playback wave form and reduce the highfrequency noise produced by the magnetic drum.

Fig. 3 shows the declining sawtooth modulated pattern produced when thearm 11 of a'potentiometer having a linearly sloping resistance gradientis rotated at 4 R. P. S. to modulate 60 cycle alternating voltageoriginating on line AC. The l5 to 1 ratio between the supply voltagefrequency and the rotational frequency of the potentiometer results inthe production of 15 amplitude-modulated sinusoidal waves in eachpattern. This pattern will be magnetically simulated on the magneticdrum, in the manner described, and subsequently reflected duringplayback operation as a voltage pattern on output terminals T1 and T2.From there, the voltage pattern will be recurrently transmitted viasuitable connections to the input terminals, also designated T1 and T2,of deflection circuits shown in Fig. 4. Input terminal T2 is groundedand the voltage with respect to ground is applied via a couplingcapacitor C10 to point a of a phase shifting network consisting ofcapacitors C11 and C12 and resistors R11 and R12. Point b of the networkgoes to ground. Points c and d of the network are its output points, andthe voltage waves appearing at one of these output points are shifted bythe network degrees out of phase with the waves appearing at the otheroutput point. R11 and R12 are variable resistors affording means wherebythe voltage waves at points c and d may be equalized in amplitude at therequired phase difference of 90 degrees. Points c and d connect,respectively, to the grids in the left halves of like dual triode tubesV1 and V2 in symmetrical vertical and horizontal deflection circuits',respectively. R13 is a conventional grid resistor to ground for the lefthalf of V1; R11 serves as a corresponding grid resistor for the lefthalf of V2. To indicate that V1 and V2 are in identical symmetricalcircuits, the corresponding anode and cathode resistors of V1 and V2 areidentified by the same reference designations.

,The two cathodes in each of V1 and V2 have a common cathode resistorR14 terminating at a negative voltage line C-. The anodes V1 and V2 aresupplied with voltage via resistors R15 and R15' from a B+ supply line.The anode lines of V1 connect to vertical deflection plates VP of acathode ray tube CR, while the anode lines of V2 connect to horizontaldeflection plates HP. Each of the tubes V1 and V2 is thus connected as aconventional phase inverter to furnish pushpull deflection potentials inresponse to the phase-shifted control voltage applied to the input gridof the tube. The coordinate deflection potentials furnished by V1 and V2mirror the applied control voltages and hence consist of sinusoidalwaves of progressively decreasing amplitude during each scanning cycle,consistent in duration with a sawtooth cycle. Due to the sinusoidal waveform of the coordinate deflection potentials and their phase differenceof 90, the electron beam in the tube CR and its trace on the face of thetube have a rotary motion. The trace motion would be completely circularwere it not for the progressive decrease in amplitude of the deflectionpotentials during the scanning cycle. Because of this progressivedecrease, the radius of the trace diminishes during the scanning cycleso that the trace describes a decreasing spiral scanning pattern orraster of the form shown in Fig. 5. During each scanning cycle, thedeflection potential amplitude decreases from a maximum sufficient tocause the trace to describe the outer revolution of the raster to aminimum value and then returns rapidly to maximum value to start a newraster at the beginning of the next cycle. Each pair of coordinatelyacting deflection voltage waves is responsible for one revolution of theraster. Hence, with l5 voltage waves per sawtooth cycle (Fig. 3)supplied to the deflection circuits, the 15 corresponding waves ofdeflection potential supplied by these circuits to the deflection platesresult in a raster with fifteen revolutions.

The potentiometer R17 between the B+ line and ground is an astigmatismcontrol for setting the final anode of the cathode ray tube at theaverage potential level of the deflection plates so that the trace willbe sharp, of minimum size, in all parts of the raster. The sources ofvoltages, other than those shown, required for operation of the cathoderay tube are entirely conventional and need not be shown.

While there have been shown and described the fundamental novel featuresof the invention as applied to a preferred embodiment, it is understoodthat various substitutions and changes in the form and details of thedevice illustrated and in its mode of operation may be made by thoseskilled in the art, Without departing from the spirit of the invention.It is intended, therefore, to be limited only as indicated by thefollowing claims.

I claim:

1. In a signal generator; an alternating current source an input linefor deriving from said source an alternating wave form input signal tobe modulated, an output line for the modulated signal, and amplitudemodulating means including a cyclically operating potentiometer havingits resistive element and slider in series connecof traverse of the`resistive element at a synchronized.

submultiple cyclic frequencyofthe quency of the input signal.

2. In a signal generator asg defined in claim 2, a mag* neticallycoercive: medium-driven. by the motor intimed relation. tov thepotentiometer cycles,l a magnetic pickup head1 for said medium, and arecording circuit coupled to. said output line for applying1 themodulated signal patterns formedk during successive potentiometer cyclesto; the pickup4 head. to eiect magnetic recording of the modulated.signal upon. said medium.

3.1 Inl a signal. generator; a power line carrying sinusoidal cyclevoltage, a circuit powered by said line to provide ak similar sinusoidalcycle input signal to be modulated, an output circuit for the modulatedsignal, and amplitude modulating means including a potentiometer having`itsresistive element and slider in series connection between saidcircuits to. receive the input signal, modulate it, andimpress. themodulated signal upon the output circuit, said resistive element havinga substantially linear resistance gradient so as to coact with thesilden upon each traverse thereof by the slider to impose a modulating,component of sawtooth form upon the input signal, va synchronous motorpowered by said line, drive connections from the motor to the slider toactuate the slider continually through successive cycles oftravalternating wave freerse of the resist-ive element in synchronizedsubmultiple frequency ratio! to they sinusoidal cycle frequency of theinputl signal,x whereby' the modulatingy saWtDoth form; is cyclically.imposed upon like series. of sinusoidalY cycles to produce repeatpatterns of sinusoidal: cycles of progressively varying amplitude withineach pattern.

4'. Thel invention as dened in claim 3, the: potentiometer being` of therotary type having its slider continllf ously rotated bythe motor totraverse the resistive element from one end tothe other and return-v tothe former end during each revolution, and impedance means across theslider and said former end of the resistive element to establish thevoltage' level of the modulated signal duringV the interval of slidermovement across the gap between said ends.

5. The invention according to claim 3, includingy a magneticallycoercive rotatable medium, al transmission;

between the motor and the medium for driving theA mediurny in integralsubmultiple ratio to the cycles of the slider, and a magnetic recordingcircuit coupled. to said output circuit to magnetically record upon asingle circular track of the medium a number of identical',Y completesignal patterns dependent on said' submultiple ratio.

ReerencesCited inthe file of this patent UNITED STATES PATENTS 2,400,791Tolson et al May 21, 1946 2,411,030 De Ryder Nov. 12, 1.946 2,618,764Reiber Nov. 18, 1952 2,656,407 Herrick et al; Oct. 20, 1953 2,660,709`Hampshire et al. Nov. 24', 1953 2,730,699 Gratian` J an. 10', 1956

